1. Field of the Disclosure
The present disclosure relates to a rotary connector mounted to a steering column of an automobile, for example, and more particularly to a rotary connector allowing a cable to be smoothly moved between a stationary case and a movable reel.
2. Description of the Related Art
In a steering column of an automobile, it is required, between a stationary unit and a rotating unit, to supply electric power for operating an airbag and to transmit switching signals from a horn switch and other various control switches. A rotary connector is used to meet such needs.
In a rotary connector disclosed in Japanese Unexamined Patent Application Publication No. 2012-209253, a movable housing is rotatably disposed inside a stationary housing, and a rotating ring member is disposed between the stationary housing and the movable housing. The stationary housing includes an internal gear, the movable housing includes a sun gear, and the rotating ring member rotatably supports a planetary gear. The planetary gear is meshed with both the internal gear and the sun gear. When the movable housing is rotated, the planetary gear is also rotated by the sun gun that is rotated together with the movable housing. Thus, the rotating ring member is rotated at a rotational speed lower than that of the movable housing.
Opposite ends of a flat cable are fixed respectively to the stationary housing and the movable housing. The flat cable is disposed to extend along an inner peripheral surface of the stationary housing, and to pass a reverse maintaining portion, which is provided in the rotating ring member, to be reversed. The flat cable is then wound over an outer peripheral surface of the movable housing.
According to the above-described rotary connector, when the movable housing is rotated, the rotating ring member is rotated at a decelerated speed following the rotation of the movable housing. Therefore, a reversing portion of the flat cable can be guided in a rotating direction by the reverse maintaining portion that is rotated together with the rotating ring member.
In a cable reel disclosed in Japanese Unexamined Patent Application Publication No. 4-333472, a flexible cable is arranged in a space between an inner peripheral surface of a stationary member and an outer peripheral surface of a movable member. The flexible cable is arranged along the inner peripheral surface of the stationary member, and after being reversed within the space, it is wound over the outer peripheral surface of the movable member. An elastic ring is disposed in the space to be gripped by the reversing flexible cable in an embraced state.
In the above-mentioned cable reel, when the movable member is rotated, a reversing portion of the flexible cable is moved in the space. At that time, however, the elastic ring gripped by the flexible cable is caused to rotate on its axis due to friction between the elastic ring and the flexible cable. Because the elastic ring moves while rotating on its axis, the reversing portion of the flexible cable can be guided by the elastic ring. As a result, a winding operation and an unwinding operation of the movable cable can be performed reliably.
In the rotary connector disclosed in Japanese Unexamined Patent Application Publication No. 2012-209253, when the movable housing is rotated, the reverse maintaining portion provided in the rotating ring member is also rotated, and the reversing portion of the flat cable is guided by the reverse maintaining portion. At that time, the reversing portion of the flat cable always slides against the reverse maintaining portion. There is hence a possibility that the flat cable may wear when used for a long term. In consideration of such a possibility, a lubricant is usually applied to the reverse maintaining portion to reduce a frictional force generated between the reverse maintaining portion and the flat cable. However, the lubricant of the type used in automobiles for that purpose needs to be superior in temperature characteristics, etc. and is very expensive. This causes a problem of increasing the cost of the rotary connector.
In the cable reel disclosed in Japanese Unexamined Patent Application Publication No. 4-333472, the elastic ring capable of freely moving in the state gripped by the reversing portion of the flexible cable is disposed in the space between the stationary member and the movable member. The elastic ring is rotated only by the action of the frictional force between the elastic ring and the flexible cable. Accordingly, if slippage occurs between the flexible cable and the elastic ring, a rotational position of the elastic ring would be instable after the occurrence of slippage. As a result, the elastic ring can no longer guide the reversing portion of the flexible cable, and the shape of the reversing portion of the flexible cable is deformed. This causes a problem that the flexible cable cannot be stably wound and unwound in the above-mentioned space.